Synthesis and luminescence properties of highly uniform SiO2@LaPO4:Eu3+ core–shell phosphors

SiO₂@LaPO₄:Eu³⁺ core–shell phosphors have been successfully synthesized by a one-step and economical wet-chemical route at low temperature. The as-obtained products were characterized by means of photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The SEM, EDS and XPS analysis indicate that SiO₂@LaPO₄:Eu³⁺ core–shell phosphors can only be synthesized in a pH range of 8–11 and the possible mechanism has been proposed. The XRD results demonstrate that the structure of LaPO₄:Eu³⁺ layers is transferred into monoclinic phase from hexagonal phase after annealing at 800 °C for 2 h. The SiO₂@LaPO₄:Eu³⁺ phosphors show strong orange–red luminescence under ultraviolet excitation. The relative emission intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles, and the optimum concentration for Eu³⁺ was determined to be 5 mol% of La³⁺ in SiO₂@LaPO₄ phosphors.     

Host-sensitized phosphorescence of Mn4+, Pr3+,4+ and Nd3+ in MgAl2Si2O8

Mn⁴⁺ doped and Pr^3+,4+, Nd³⁺ co-doped MgAl₂Si₂O₈-based phosphors were first of all synthesized about 1300 °C. They were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 610–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the intrinsic d–d transitions of Mn⁴⁺.     

Photoluminescence properties of MgAl2O4:Dy powder phosphor

Trivalent dysprosium (Dy³⁺) activated magnesium alluminate phosphors were synthesized by high temperature solid state reaction method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting phosphors. The results show that the obtained MgAl₂O₄:Dy³⁺ phosphors have good crystallinity, spherical morphology with sizes ranged from 120 to 140 nm and strong blue emission under an excitation of 258 nm. The emission spectrum of this phosphor consists of two emission bands: blue band and yellow band, and the emission intensity of the former is stronger than that of the later. Luminescence quenching is explained and the corresponding luminescence mechanisms have been proposed.     

Comparative study of Ca3Bi(PO4)3:Eu3+ phosphors prepared by three methods

Ca₃Bi(PO₄)₃:Eu³⁺ phosphors were synthesized by solid-state (SS) reaction, co-precipitation (CP) and sol–gel methods. The resulting phosphors were well characterized by X-ray diffraction, field-emission scanning electron microscopy and photoluminescence spectra. The X-ray diffraction results suggested that the pure phase of Ca₃Bi(PO₄)₃:Eu³⁺ can be obtained by SS reaction and CP method. The phosphors obtained by CP method showed more homogeneous, agglomerate-free particles. The samples obtained by the CP method showed the highest emission intensity among the three methods which fired at 1,000 °C for 2 h. It was showed that the CP method was the most respected process for the preparation of Ca₃Bi(PO₄)₃:Eu³⁺ phosphors.     

Hydrothermal synthesis and photoluminescence of SrWO4:Tb novel green phosphor

Tb³⁺-doped SrWO₄ phosphors with a scheelite structure have been prepared by hydrothermal reaction. X-ray powder diffraction, field-emission scanning electron microscopy, photoluminescence excitation and emission spectra and decay curve were used to characterize the resulting samples. Scanning electron microscopy image showed that the obtained SrWO₄:Tb³⁺ phosphors appeared to be nearly spherical and their sizes ranged from 1 to 3 μm. Photoluminescence spectra indicated the phosphors emitted strong green light centered at 545 nm under ultraviolet light excitation. Because 12 at.% SWO₄:Tb³⁺ phosphor exhibits intensive green emission under 254 nm excitation in comparison with the commercial green fluorescent lamp phosphor (LaPO₄:Ce,Tb), the excellent luminescence properties make it a new promising green phosphor for fluorescent lamps application.     

Synthesis and luminescence properties of monodisperse SiO2@SiO2:Eu3+ microspheres

Monodisperse core–shell structured SiO₂@SiO₂:Eu³⁺ microspheres were synthesized in a seeded growth way. In that way, a thin shell of Eu³⁺-doped silica was grown on the prepared monodisperse silica colloids. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), thermal analysis (TGA-DSC) and photoluminescence (PL) spectroscopy. The results reveal that the SiO₂ spheres have been successfully coated by SiO₂:Eu³⁺ phosphors and the obtained SiO₂@SiO₂:Eu³⁺ particles have perfect spherical shape with narrow size distribution. Additionally, the monodisperse SiO₂@SiO₂:Eu³⁺ microspheres exhibit considerably strong photoluminescence (PL) of Eu³⁺ under the excitation of 393 nm compared with the SiO₂:Eu³⁺ samples with polydispersed or irregular shapes and sizes obtained by base-catalyzed Stöber method. Furthermore, the PL intensity increases with the increasing of Eu³⁺ concentration in SiO₂ microspheres shell, and concentration quenching occurs when Eu³⁺ concentration exceeds 5.0 mol%.     

Luminescence studies on Eu<Superscript>2+</Superscript> and Tb<Superscript>3+</Superscript> doped Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript> phosphors

Eu²⁺ and Tb³⁺ doped Ca₂MgSi₂O₇ phosphors were synthesized by conventional solid-state reaction. The phase formation was confirmed by X-ray powder diffraction technique and refined lattice parameters were calculated by rietveld refinement process using Celref v3. The photoluminescence (PL) excitation and emission spectra were investigated. The phosphors exhibited broaden green emitting luminescence peaking at 520 nm when excited at 374 nm source. Morphological studies were carried out using Scanning electron microscopy (SEM) images of the sample with optimum PL emission. The dependence of photoluminescence intensity on co-dopant concentration and the kinetic parameters were also reported. Time resolved fluorescence spectroscopy (TRFS) is used to investigate the decay in luminescence signals with respect to time. The sample proved to be a good long lasting material, which makes it useful in emergency signs, textile printing, textile exit sign boards and electronic instrument dial pads etc.     

Hydrothermal synthesis and photoluminescence properties of Gd2Zr2O7:Tb phosphors

This paper presents hydrothermal synthesis, characterization, and photoluminescence (PL) properties of novel green-emitting phosphors, Gd₂Zr₂O₇:Tb³⁺. Their crystal structure, morphology and photoluminescence properties were investigated by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM) and fluorescence spectrophotometer. The results revealed that one-dimensional Gd₂Zr₂O₇:Tb³⁺ nanorods with diameter of about 30 nm and length of 150-300 nm were formed, and the products exhibited a fluorite-type structure. PL study revealed that Gd₂Zr₂O₇:Tb³⁺ phosphors presented dominant green emission luminescence, which was attributed to the transitions from ⁵D₄ excited states to ⁷F_J (J = 3-6) ground states of Tb³⁺. The luminescence intensity of Gd₂Zr₂O₇:Tb³⁺ with different Tb³⁺ concentration was also investigated and reported, and an obvious concentration quenching was observed when Tb³⁺ ion concentration was 5 at.%.     

Controlled synthesis and optical properties of BaFBr:Eu2+ crystals via ethanol/water solutions

BaFBr:Eu²⁺ crystals with different structures were successfully fabricated via a simple precipitation method using ethanol/water mixtures as solvents. The amount of ethanol in the solvent mixtures played a significant role in the formation of final products, enabling the well-controlled growth of the BaFBr crystals. A possible formation mechanism was proposed based on the results of controlled experiments. The phases and morphologies of the resulting samples were systematically investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED) and elementary analysis. The optical properties of the annealed BaFBr:Eu²⁺ nano-cuboids were investigated using photoluminescence (PL), photo-stimulated luminescence spectroscopy (PSL) and kinetic decays. Faster decay behaviors demonstrate that these BaFBr:Eu²⁺ phosphors are promising materials for applications in optical storage fields. Furthermore, it is envisaged that this environmentally benign method can be extended to prepare other fluoride halides.     

Synthesis and luminescence properties of a novel UV-emitting phosphor Sr<Subscript>3</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript>:Ce<Superscript>3+</Superscript>

The ultraviolet (UV)-emitting Sr₃P₄O₁₃:Ce³⁺ phosphors were synthesized via the solid-state reaction method, and their structural, morphological and luminescence properties were characterized by X-ray diffraction analysis, scanning electron microscopy, photoluminescence spectroscopy. The obtained results indicate that these phosphors can be effectively excited by short-wavelength ultraviolet (<300 nm), and exhibit long-wavelength ultraviolet (300–380 nm) emission with nanosecond-level fluorescence lifetime corresponding to the parity-allowed 5d–4f transitions of Ce³⁺. The concentration-quenching phenomenon of Ce³⁺ in Sr₃P₄O₁₃ host was also studied, in which the critical energy transfer distance between Ce³⁺ ions and concentration quenching mechanism were determined.     

Effect of Al ions on fluorescence properties of YPO4: Eu phosphors

Different concentrations of Al³⁺-doped YPO₄:Eu_0.05 powder phosphors have been synthesized by the conventional solid state reaction method and are characterized by X-ray diffraction (XRD), field emission scanning electronic microscopy (FESEM), photoluminescence excitation (PLE) and emission (PL) investigations. The influence of Al³⁺-doping on crystallinity, grain size and PL intensity of the YPO₄:Eu phosphors has been investigated. These characteristics are found improved with increase in concentration of Al³⁺ ions from 0.00 to 0.10 mol and then decreased for higher concentrations. The results are discussed in comparison with earlier reported similar works.     

Synthesis,photoluminescence and mechanoluminescence properties of Eu<Superscript>3+</Superscript> ions activated Ca<Subscript>2</Subscript>Gd<Subscript>2</Subscript>W<Subscript>3</Subscript>O<Subscript>14</Subscript> phosphors

A new series of Eu³⁺ ions-activated calcium gadolinium tungstate [Ca₂Gd₂W₃O₁₄] phosphors were synthesized by conventional solid-state reaction method. The X-ray diffraction patterns of the powder samples indicate that the Eu³⁺: Ca₂Gd₂W₃O₁₄ phosphors are of tetragonal structure. The prepared phosphors were well characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), and mechanoluminescence (ML) spectra. PL spectra of Eu³⁺: Ca₂Gd₂W₃O₁₄ powder phosphors have shown strong red emission at 615 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ _exci = 392 nm (⁷F₀ → ⁵L₆). The energy transfer from tungstate groups to europium ions has also reported. Mechanoluminescence studies of Eu³⁺: Ca₂Gd₂W₃O₁₄ phosphors have also been explained systematically.     

Improvement of morphology and luminescence of CaS:Eu<Superscript>2+</Superscript> red-emitting phosphor particles via carbon-containing additive strategy

CaS:Eu²⁺ red-emitting phosphors particles, were prepared by the precipitation method, followed by sintering in the atmosphere over the mixture of sulfur powder, Na₂CO₃, and carbon-containing compounds such as tartaric acid, citric avid, glucose, and cane sugar. The structure, morphology and photoluminescence performance of the as-prepared samples were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectrum (PL), respectively. The influences of carbon-containing additives on its crystallization behavior, morphology, and enhancement in luminescence of CaS:Eu²⁺ particles were studied. CaS:Eu²⁺ particles without additive show inhomogeneous, rough and aggregation with the size of 75–125 nm, but the spherical particles with mean size of about 110 nm were obtained by adding carbon-containing compounds. Compared with phosphor without additive, the addition of carbon-containing materials induced a remarkable increase of PL, in the order of cane sugar, glucose, citric acid, and tartaric acid. This enhancement is duo to the improvement of crystallinity, particle morphology and size distribution of the samples by adding carbon-containing additive.     

Hydrothermal synthesis and luminescence properties of core-shell-structured PS@SrCO<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript> spherical particles

Nanocrystalline SrCO₃:Tb³⁺ phosphor layers were coated on monodisperse and spherical polystyrene particles by a typical hydrothermal synthesis without further annealing treatment, resulting in the formation of core-shell-structured polystyrene@SrCO₃:Tb³⁺ particles. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, as well as lifetimes were employed to characterize the resulting composite particles. Under ultraviolet excitation, the polystyrene@SrCO₃:Tb³⁺ phosphors show the characteristic ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission lines with green emission ⁵D₄–⁷F₅ (544 nm) as the most prominent group. The obtained core-shell phosphors are potentially applied in fluorescent lamps.     

Molten salt synthesis and photoluminescence properties of novel red emitting phosphors Ba5(VO4)3Cl:Eu3+,K+

A series of Ba₅(VO₄)₃Cl:Eu³⁺,K⁺ phosphors have been synthesized by the molten salt synthesis method. The crystalline structure, morphology, photoluminescence properties and lifetimes were characterized using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and photoluminescence spectroscopy, respectively. XRD indicates that the Ba₅(VO₄)₃Cl:Eu³⁺,K⁺ phosphors are synthesized successfully via molten salt method. SEM image demonstrates that the obtained phosphors have hexagonal polyhedron morphology. The photoluminescence spectra reveal that the as-prepared phosphors exhibit a bright red emission under the excitation of blue or near ultraviolet light. The concentration quenching was also investigated, and the dipole–dipole interaction is responsible for the concentration quenching of fluorescence emission of Eu³⁺ ions in Ba₅(VO₄)₃Cl phosphor. The present work suggests that the Ba₅(VO₄)₃Cl:Eu³⁺,K⁺ phosphors would be a potential candidate for light emitting devices.     

Synthesis and luminescence properties of YVO4:Eu cobblestone - like microcrystalline phosphors obtained from the mixed solvent - thermal method

The mixed solvent-thermal method has been developed for the synthesis of YVO₄:Eu³⁺ luminescent materials in the N, N-dimethylformamide (DMF)/ de-ionized water (DIW) solution. The samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscope (TEM), UV/vis absorption and photoluminescence spectroscopies. The results demonstrate that we have obtained the uniform YVO₄:Eu³⁺ cobblestone - like microcrystalline phosphors in the mixed solution of DMF and DIW, which are different to the as-obtained YVO₄:Eu³⁺ nanoparticles in pure DIW. And the as - prepared YVO₄:Eu³⁺ microcrystalline particles are composed of numerous nanoparticles. The assembling phenomenon of the nanoparticles is strongly affected by the pH value of the solution and the volume ratio of DMF/DIW. Under UV excitation, the samples can emit the bright red light. While, the photoluminescence (PL) intensities of YVO₄:Eu³⁺ show some difference for samples obtained under the different reaction conditions. This is because that different microstructures of samples result in different combinative abilities between the surface and the adsorbed species so as to produce the different quenching abilities to the emission from Eu³⁺ ions.     

The comparison: photoluminescence and afterglow behavior in CaSnO<Subscript>3</Subscript>:Dy<Superscript>3+</Superscript> and Ca<Subscript>2</Subscript>SnO<Subscript>4</Subscript>:Dy<Superscript>3+</Superscript> phosphors

This paper reports the comparison of photoluminescence and afterglow behavior of Dy³⁺ in CaSnO₃ and Ca₂SnO₄ phosphors. The samples containing CaSnO₃ and Ca₂SnO₄ were prepared via solid-state reaction. The properties have been characterized and analyzed by utilizing X-ray diffraction (XRD), photoluminescence spectroscope (PLS), X-ray photoelectron spectroscopy (XPS), afterglow spectroscopy (AS) and thermal luminescence spectroscope (TLS). The emission spectra revealed that CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors showed different photoluminescence. The Ca₂SnO₄:Dy³⁺ phosphor showed a typical ⁴F_9/2 to ⁶H_j energy transition of Dy³⁺ ions, with three significant emissions centering around 482, 572 and 670 nm. However, the CaSnO₃:Dy³⁺ phosphor revealed a broad T₁ → S₀ transitions of Sn²⁺ ions. The XPS demonstrate the existence of Sn²⁺ ions in CaSnO₃ phosphor caused by the doping of Dy³⁺ ions. Both the CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors showed a typical triple-exponential afterglow when the UV source switched off. Thermal simulated luminescence study indicated that the persistent afterglow of CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors was generated by the suitable electron or hole traps which were resulted from the doping the calcium stannate host with rare-earth ions (Dy³⁺).     

Luminescence properties of ZnO/TiO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript> nanocomposite activated by Eu<Superscript><Emphasis Type="Bold">3</Emphasis><Emphasis Type="Bold">+</Emphasis></Superscript> and their spectroscopic analysis

A new type of novel orange-red emitting Eu-doped ZnO/TiO ₂ nanocomposite phosphors have been synthesized by simple low temperature co-precipitation route. Structure and morphology of the prepared sample have been investigated using X-ray diffraction and field emission scanning electron microscopy (FESEM) techniques. XRD pattern confirmed the presence of both phases of ZnO and TiO ₂ simultaneously. The luminescence properties, such as photoluminescence (PL) excitation and emission spectra, Judd–Ofelt parameters, CIE colour coordinates and the dependence of luminescence intensity on the doping level were investigated. The luminescence spectrum characteristics of Eu ³⁺ ions have a strong dependence on Eu ³⁺ doping levels as well as ZnO/TiO ₂ ratio variations. The photoluminescence results indicate that these phosphors could be efficiently excited by near-ultraviolet radiation, which causes emissions in orange–red regions.     

Synthesis and luminescent properties of spindle-like CaWO4:Sm3+ phosphors

Spindle-like CaWO₄:Sm³⁺ phosphors were prepared via a Polyvinylpyrrolidone (PVP)-assisted sonochemical process, and characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectroscopy (PL). The XRD results suggested that the prepared samples are single-phase. The FE-SEM images indicated that the prepared CaWO₄:Sm³⁺ phosphors are composed of many spindles with maximum average diameter of 150 nm and maximum average length of 500 nm. Under 404 nm excitation, the characteristic emissions corresponding to ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) transitions of Sm³⁺ in CaWO₄ phosphors were observed. The color coordinates for 1 mol% Sm³⁺ doped CaWO₄ phosphor were calculated to be (0.595, 0.404). The fluorescent concentration quenching of Sm³⁺ doped spindle-like phosphors was studied based on the Van Uitert's model, and it was found that the electric dipole–dipole (D–D) interaction is the dominant energy transfer mechanism between Sm³⁺ ions in the CaWO₄:Sm³⁺ phosphors. The critical energy transfer distance was estimated.     

Synthesis,characterization and formation mechanism of monodispersed Gd<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Eu<Superscript>3+</Superscript> nanocrystals

Monodispersed Gd₂O₂S:Eu³⁺ nanostructures with tunable morphologies have been selectively fabricated by solvothermal method in the presence of stable inorganic precursors avoiding metalorganic precursors. The size and morphology of the products were controlled successfully by adjusting the reaction conditions. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). The corresponding UV absorption and photoluminescence excitation spectra show a significant blue-shift confirming the quantum confinement effect. A possible growth mechanism for the formation of monodispersed Gd₂O₂S:Eu³⁺ nanocrystals has been proposed. The luminescence mechanism and the size dependence of their fluorescence properties are also discussed.